Liquid crystal aligning agent

ABSTRACT

The present invention relates to a treating agent for liquid crystal alignment, which comprises a polyamic acid compound having a reduced viscosity of from 0.05 to 5.0 dl/g (in N-methylpyrrolidone at a temperature of 30° C. at a concentration of 0.5 g/dl) and containing repeating units represented by the general formula [I]:                    
     (wherein R 1  is a tetravalent organic group constituting a tetracarboxylic acid which has an alicyclic structure having from 2 to 5 rings condensed and wherein all the carbonyl groups are directly bonded to the alicyclic structure and said carbonyl groups are not bonded to adjacent carbon atoms in the alicyclic structure, and R 2  is a bivalent organic group constituting a diamine), or a polyimide resin obtained by imidizing said polyamic acid compound, and a liquid crystal alignment film and a liquid crystal device employing it.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a treating agent for liquid crystalalignment to be used for liquid crystal devices such as a liquid crystaldisplay device, and a liquid crystal alignment film and a liquid crystaldevice utilizing it. More particularly, it relates to a treating agentfor liquid crystal alignment, which is excellent in the printingproperties to a substrate, which will be free from separation from thesubstrate during rubbing, which provides an alignment film which will beless likely to be damaged by rubbing, and which provides an excellentvoltage holding property when a liquid crystal cell is operated, and aliquid crystal alignment film and a liquid crystal device employing it.

2. Background Art

A liquid crystal display device is a display device utilizing anelectrooptical change of liquid crystal, and as an apparatus, it issmall in size and light in weight and has an attractive feature suchthat the power consumption is small. Accordingly, in recent years, ithas undergone remarkable developments as a display device for varioustypes of displays. Among them, an electric field effect type liquidcrystal display device of twisted nematic type (TN type) is a typicalone, wherein nematic liquid crystal having positive dielectricanisotropy is employed, liquid crystal molecules are aligned at therespective interfaces of a pair of electrode substrates disposed to faceeach other, in parallel with the substrates, and the substrates arecombined so that the alignment directions of liquid crystal moleculeswill cross each other. Further, among the TN type liquid crystaldevices, an active matrix operation system utilizing a TFT (Thin FilmTransistor) having excellent display performance, has been activelydeveloped.

In such a TN type liquid crystal display device, it is important thatlong axes directions of liquid crystal molecules are uniformly alignedin parallel on the substrate surface and further that liquid crystalmolecules are aligned with a certain tilt angle to the substrate. As amethod for aligning liquid crystal molecules in such a manner, a rubbingtreatment has been usually employed. The rubbing treatment is a methodwherein an organic coating film is formed on the surface of a substrate,and the surface is rubbed with a cloth of e.g. cotton, nylon orpolyester in a predetermined direction, so that liquid crystal moleculesare aligned in the direction of rubbing. By this method, stabilizedalignment can be obtained relatively easily, and industrially, thismethod is mainly employed. As the organic film, polyvinyl alcohol,polyoxyethylene, polyamide or polyimide may, for example, be mentioned.However, from the viewpoint of chemical stability, thermal stability,etc., polyimide is most commonly employed.

With respect to the treating agent for liquid crystal alignment using apolyimide, commonly, a varnish having a solvent-soluble type polyimidedissolved in a solvent is coated on a substrate followed by baking toform a polyimide film, and then rubbing treatment is carried out thereonto obtain a liquid crystal alignment film, or a solution of a polyamicacid as a polyimide precursor, is coated on a substrate, generallyfollowed by baking at a temperature of at least 150° C. for imidization,and then rubbing treatment is carried out thereon to obtain a liquidcrystal alignment film.

As basic properties required for such an alignment film, the tilt angleof liquid crystal molecules, the voltage holding ratio andcharge-accumulation property by direct current voltage, may, forexample, be mentioned, and the voltage holding property is an importantproperty from the viewpoint of the constitution of the device,particularly in the TFT display system. It has been known that suchproperties of an alignment film greatly depend on the liquid crystalspecies to be used, but they are influenced also by the structure of thepolyimide to be used. Accordingly, it has been attempted to improve filmproperties by variously selecting the structure of the polyimide.

With respect to the liquid crystal alignment film formed by asolvent-soluble polyimide, it has been known that usually baking can becarried out at a low temperature and excellent voltage holding propertycan be obtained. However, there has been such problems that the tiltangle is not adequate or its stability is not adequate, or thecharge-accumulation property is not adequately low. Further, there hasbeen such a problem that e.g. the printing properties and adhesiveproperties to a substrate are poor.

On the other hand, the liquid crystal alignment film using a polyamicacid as a polyimide precursor, has such advantages that a high and morestable tilt angle can be obtained and the charge-accumulation propertyby the direct-current voltage can be made small, and further, theprinting properties and adhesive properties to a substrate areexcellent. However, it has such drawbacks that the voltage holdingproperty is poor, or the solvent resistance at the surface of the filmis poor in the case where the imidization degree is insufficient.

From the viewpoint of the production of a liquid crystal display device,properties such as adhesive properties and printing properties of thealignment film to a substrate, and rubbing resistance, are important.Particularly in rubbing treatment, which is an industrially employedmethod for treating liquid crystal alignment, there are such problemsthat the liquid crystal alignment film may be separated off from thesubstrate due to abrasion during rubbing, or the liquid crystalalignment film may be damaged, thus influencing over display properties.

Further, from the viewpoint of reliability and environmental resistanceof the display device, an alignment treating agent having excellentalignment film properties, particularly voltage holding property, at ahigh temperature, has been required. Namely, a fluorine type liquidcrystal is widely used for a display device of TFT operation system, andit has been known that usually the voltage holding property tends to behigh in the case of using this liquid crystal. However, even in a casewhere the voltage holding ratio is high at the beginning, a displayfailure such as display unevenness may be caused during a long-term useof the liquid crystal display device in some cases, and the reliabilityis not adequately high. Further, in the case where liquid crystal forlow-voltage operation is used, the voltage holding property maydecrease, and an adequately high reliability can hardly be obtained,such being problematic.

As mentioned above, both solvent-soluble polyimide and polyamic acidhave merits and demerits which are in an antinomic relation to eachother as a liquid crystal alignment film, and it is not necessarily easyto satisfy all properties required as a liquid crystal alignment film.However, a treating agent for liquid crystal alignment, which isparticularly excellent in the printing properties to a substrate, theadhesive properties and rubbing resistance, and which has a highreliability, has been desired.

The present invention has been made to overcome the above problems.Namely, it is an object of the present invention to provide a treatingagent for liquid crystal alignment, which is excellent in the adhesiveproperties and the printing properties to a substrate, which is freefrom separation from the substrate during rubbing, which provides analignment film which is less likely to be damaged by rubbing, and whichprovides an excellent voltage holding property regardless of the type ofliquid crystal when a liquid crystal cell is operated.

DISCLOSURE OF THE INVENTION

The present inventors have conducted extensive studies to overcome theabove problems, and as a result, the present invention has beenaccomplished. Namely, the present invention relates to a treating agentfor liquid crystal alignment, which comprises a polyamic acid compoundhaving a reduced viscosity of from 0.05 to 5.0 dl/g (inN-methylpyrrolidone at a temperature of 30° C. at a concentration of 0.5g/dl) and containing repeating units represented by the general formula[I]:

(wherein R¹ is a tetravalent organic group constituting atetracarboxylic acid which has an alicyclic structure having from 2 to 5rings condensed and wherein all the carbonyl groups are directly bondedto the alicyclic structure and said carbonyl groups are not bonded toadjacent carbon atoms in the alicyclic structure, and R² is a bivalentorganic group constituting a diamine), or a polyimide compound obtainedby imidizing said polyamic acid compound, and a liquid crystal alignmentfilm and a liquid crystal display device employing it.

BEST MODE FOR CARRYING OUT THE INVENTION

R¹ in the general formula [I] of the present invention is preferably atetravalent organic group constituting a tetracarboxylic acidrepresented by the general formula [II]:

(wherein each of X¹, X², X³ and X⁴ which are independent of one another,is a single bond or a methylene group, and m is an integer of from 1 to3). More preferably, m in the general formula [II] is 1 or 2,particularly preferably m is 1.

Specific examples of the tetracarboxylic acid having the tetravalentorganic group constituting the tetracarboxylic acid represented by thegeneral formula [II] wherein m is 1 of the present invention, includetetracarboxylic acids such asbicyclo[3,3,0]-octane-2,4,6,8-tetracarboxylic acid:

bicyclo[4,3,0]nonane-2,4,7,9-tetracarboxylic acid:

bicyclo[4,4,0]decane-2,4,7,9-tetracarboxylic acid:

bicyclo[4,4,0]decane-2,4,8,10-tetracarboxylic acid:

and dianhydrides thereof. Specific examples of the tetracarboxylic acidwherein m is 2, include tetracarboxylic acids such astricyclo[6.3.0.0<2,6>]undecane-3,5,9,11-tetracarboxylic acid:

and dianhydrides thereof. Among them, more preferred isbicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic acid from the viewpoint ofstability of the liquid crystal alignment.

Further, these tetracarboxylic acids have structural isomers, and onetype of the isomers may be used or a mixture of the isomers may be used.Particularly, bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic acid hasisomers as represented by the formulae [IV], [V] and [VI]:

One type of the isomers may be used, or a mixture thereof may be used,to obtain the effect of the present invention. However, from theviewpoint of the polymerization reactivity, the content of the isomer[IV] is preferably at least 90%, more preferably at least 95%.

Bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic acid and its dianhydridecan be synthesized, for example, by the following method. Namely,2,5-novolunadiene and dicyclopentadiene are reacted in an autoclave at190° C. for 20 hours to synthesizetetracyclo[6.2.1.1<3,6>0.0<2,7>]dodeca-4,9-diene. This is subjected toozone oxidation in methanol at a temperature of at most −30° C.,followed by oxidative destruction by using hydrogen peroxide in asolvent mixture of formic acid and acetic acid to obtainbicyclo[3.3.0]octane-2,4,6,8-tetracarboxylic acid (hereinafter referredto simply as BOTC), and this tetracarboxylic acid is subjected to heattreatment by acetic anhydride to obtainbicyclo[3.3.0]octane-2,4,6,8-tetracarboxylic dianhydride. Further, BOTCcan be obtained by oxidation oftetracyclo[6.2.1.1<3,6>0.0<2,7>]dodeca-4,9-diene by potassiumpermanganate.

In the present invention, it is essential that a polyamic acid havingrepeating units using a tetracarboxylic acid component which has analicyclic structure having from 2 to 5 rings condensed and wherein allthe carbonyl groups are directly bonded to the alicyclic structure andsaid carbonyl groups are not bonded to adjacent carbon atoms in thealicyclic structure, or a polyimide, is incorporated. Thistetracarboxylic acid component is incorporated in an amount ofpreferably at least 10 mol % based on the total tetracarboxylic acidcomponent, and another tetracarboxylic acid component may becopolymerized therewith within a range of not impairing the object ofthe present invention.

Specific examples of which include aromatic tetracarboxylic acids suchas pyromellitic acid, 2,3,6,7-naphthalenetetracarboxylic acid,1,2,5,6-naphthalenetetracarboxylic acid,1,4,5,8-naphthalenetetracarboxylic acid,2,3,6,7-anthracenetetracarboxylic acid,1,2,5,6-anthracenetetracarboxylic acid,3,3′,4,4′-biphenyltetracarboxylic acid, 2,3,3′,4-biphenyltetracarboxylicacid, bis(3,4-dicarboxyphenyl)ether,3,3′,4,4′-benzophenonetetracarboxylic acid,bis(3,4-dicarboxyphenyl)sulfone, bis(3,4-dicarboxyphenyl)methane,2,2-bis(3,4-dicarboxyphenyl)propane,1,1,1,3,3,3-hexafluoro-2,2′-bis(3,4-dicarboxyphenyl)propane,bis(3,4-dicarboxyphenyl)dimethylsilane,bis(3,4-dicarboxyphenyl)diphenylsilane, 2,3,4,5-pyridinetetracarboxylicacid and 2,6-bis(3,4-dicarboxyphenyl)pyridine, alicyclic tetracarboxylicacids such as 1,2,3,4-cyclobutanetetracarboxylic acid,1,2,3,4-cycloheptanetetracarboxylic acid,2,3,4,5-tetrahydrofurantetracarboxylic acid,1,2,4,5-cyclohexanetetracarboxylic acid,3,4-dicarboxy-1-cyclohexylsuccinic acid and3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid, andaliphatic tetracarboxylic acids such as butanetetracarboxylic acid. Theymay be used as a mixture of at least two.

The diamine having the structure of R² in the general formula [I] is notparticularly limited, and its specific examples include aromaticdiamines such as p-phenylenediamine, m-phenylenediamine,2,5-diaminotoluene, 2,6-diaminotoluene, 4,4′-diaminobiphenyl,3,3′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dimethoxy-4,4′-diaminobiphenyl,diaminodiphenylmethane, diaminodiphenylether,2,2′-diaminodiphenylpropane, bis(3,5-diethyl-4-aminophenyl)methane,diaminodiphenylsulfone, diaminobenzophenone, diaminonaphthalene,1,4-bis(4-aminophenoxy)benzene, 1,4,-bis(4-aminophenyl)benzene,9,10-bis(4-aminophenyl)anthracene, 1,3-bis(4-aminophenoxy)benzene,4,4′-bis(4-aminophenoxy)diphenylsulfone,2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis(4-aminophenyl)hexafluoropropane and2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, alicyclic diaminessuch as bis(4-aminocyclohexyl)methane andbis(4-amino-3-methylcyclohexyl)methane, and aliphatic diamines such as1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane and1,6-diaminohexane, and silicon diamines such as

(wherein m is an integer of from 1 to 10). Further, diamines having along chain alkyl group such as 4,4′-diamino-3-dodecyldiphenylether,1-dodecanoxy-2,4′-diaminobenzene, 1,1-bis(4-aminophenyl)cyclohexane and2,2-bis[4-(4-aminophenoxy)phenyl]octane, may be used. A mixture of atleast two of these diamines may be used.

Further, although such diamine components are not particularly limited,a diamine having a long chain alkyl group or fluorine-containing alkylgroup with a carbon number of from 6 to 20, is contained in an amount ofat least 1 mol %, preferably from 5 mol % to 100 mol %, based on R², inorder to obtain the tilt angle of liquid crystal. Diamines having such astructure include, in addition to diamines having a long chain alkylgroup, such as 4,4′-diamino-3-dodecyldiphenylether,1-dodecanoxy-2,4-diaminobenzene, 1,1-bis(4-aminophenyl)cyclohexane and2,2-bis[4-(4-aminophenoxy)phenyl]octane, diamines such as4-(4-trans-n-propylcyclohexylphenoxy)-1,3-diaminobenzene,4-(4-trans-n-butylcyclohexylphenoxy)-1,3-diaminobenzene,4-(4-trans-n-heptylcyclohexylphenoxy)-1,3-diaminobenzene,4-(4-trans-n-pentylcyclohexylphenoxy)-1,3-diaminobenzene,4-trans-n-propylbicyclohexyl-3,5-diaminobenzoate,4-trans-n-butylbicyclohexyl-3,5-diaminobenzoate and4-trans-n-pentylbicyclohexyl-3,5-diaminobenzoate, and the followingcompounds:

It is essential that the alignment treating agent of the presentinvention contains a polyamic acid containing repeating units using atetracarboxylic acid component which has an alicyclic structure havingfrom 2 to 5 rings condensed and wherein all the carbonyl groups aredirectly bonded to the alicyclic structure and said carbonyl groups arenot bonded to adjacent methylene groups in the alicyclic structure, or apolyimide. Further, a polyamic acid represented by the general formula[VII]:

(wherein R³ is a tetravalent organic group constituting atetracarboxylic acid, and R⁴ is a bivalent organic group constituting adiamine) having a reduced viscosity of from 0.05 to 5.0 dl/g (inN-methylpyrrolidone at a temperature of 30° C., at a concentration of0.5 g/dl) may be mixed therewith.

In this case, the mixing ratio is preferably such that the polyamic acidor the polyimide having repeating units of the present invention is atleast 10 wt %, preferably from 10 to 80 wt %, based on the total polymerweight, in order to obtain uniform alignment of liquid crystal.

Specific examples of the tetracarboxylic acid constituting R³ in thegeneral formula [VII] include aromatic tetracarboxylic acids such aspyromellitic acid, 2,3,6,7-naphthalenetetracarboxylic acid,1,2,5,6-naphthalenetetracarboxylic acid,1,4,5,8-naphthalenetetracarboxylic acid,2,3,6,7-anthracentetracarboxylic acid, 1,2,5,6-anthracenetetracarboxylicacid, 3,3′,4,4′-biphenyltetracarboxylic acid,2,3,3′,4-biphenyltetracarboxylic acid, bis(3,4-dicarboxyphenyl)ether,3,3′,4,4′-benzophenonetetracarboxylic acid,bis(3,4-dicarboxyphenyl)sulfone, bis(3,4-dicarboxyphenyl)methane,2,2-bis(3,4-dicarboxyphenyl)propane,1,1,1,3,3,3-hexafluoro-2,2′-bis(3,4-dicarboxyphenyl)propane,bis(3,4-dicarboxyphenyl)dimethylsilane,bis(3,4-dicarboxyphenyl)diphenylsilane, 2,3,4,5-pyridinetetracarboxylicacid and 2,6-bis(3,4-dicarboxyphenyl)pyridine, alicyclic tetracarboxylicacids such as 1,2,3,4-cyclobutanetetracarboxylic acid,1,2,3,4-cycloheptanetetracarboxylic acid,2,3,4,5-tetrahydrofurantetracarboxylic acid,1,2,4,5-cyclohexanetetracarboxylic acid,3,4-dicarboxy-1-cyclohexylsuccinic acid,3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic acid andbicyclo[3,3,0]-octane-2,4,6,8-tetracarboxylic acid, and aliphatictetracarboxylic acids such as butanetetracarboxylic acid. They may beused as a mixture of at least two. An alicyclic tetracarboxylic acid ispreferred to obtain a high voltage holding property, and more preferredis 1,2,3,4-cyclobutanetetracarboxylic acid orbicyclo[3,3,0]-octane-2,4,6,8-tetracarboxylic acid.

Specific examples of R⁴ in the general formula [VII] include aromaticdiamines such as p-phenylenediamine, m-phenylenediamine,2,5-diaminotoluene, 2,6-diaminotoluene, 4,4′-diaminobiphenyl,3,3′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dimethoxy-4,4′-diaminobiphenyl,diaminodiphenylmethane, diaminodiphenylether,2,2′-diaminodiphenylpropane, bis(3,5-diethyl-4-aminophenyl)methane,diaminodiphenylsulfone, diaminobenzophenone, diaminonaphthalene,1,4-bis(4-aminophenoxy)benzene, 1,4,-bis(4-aminophenyl)benzene,9,10-bis(4-aminophenyl)anthracene, 1,3-bis(4-aminophenoxy)benzene,4,4′-bis(4-aminophenoxy)diphenylsulfone,2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis(4-aminophenyl)hexafluoropropane and2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, alicyclic diaminessuch as bis(4-aminocyclohexyl)methane andbis(4-amino-3-methylcyclohexyl)methane, and aliphatic diamines such as1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane and1,6-diaminohexane, and silicon diamines such as

(wherein m is an integer of from 1 to 10). Further, diamines having along chain alkyl group, such as 4,4′-diamino-3-dodecyldiphenylether,1-dodecanoxy-2,4′-diaminobenzene, 1,1-bis(4-aminophenyl)cyclohexane and2,2-bis[4-(4-aminophenoxy)phenyl]octane, may be used. A mixture of atleast two of these diamines may also be used.

The treating agent for liquid crystal alignment of the present inventionmay be used as a polyamic acid obtained by reacting an acid dianhydridewith a diamine in a solvent. However, it is preferred to convert thepolyamic acid into an imide in the solvent to obtain a solvent-solublepolyimide, in order to obtain a high voltage holding property at a hightemperature. In such a case, the imidization degree a% is 0<a≦100%, andin order to obtain a higher voltage holding property, it is preferably20≦a≦100%, more preferably 50≦a≦100%.

In the case where the treating agent for liquid crystal alignment of thepresent invention is used as a solution of a polyamic acid as apolyimide precursor, and in the case where it is used as a solution ofthe polyamic acid represented by the general formula [VII], the methodfor producing the polyamic acid is not particularly limited. However, itis common to react a tetracarboxylic dianhydride with a diamine in anorganic polar solvent. In this case, the molar ratio of thetetracarboxylic dianhydride to the diamine is preferably from 0.8 to1.2. The closer to 1 the molar ratio, the higher the polymerizationdegree of the polymer to be produced, similar to a conventionalcondensation polymerization reaction. If the polymerization degree istoo low, the strength of the polyimide coating film tends to beinadequate, and if the polymerization degree is too high, workabilityduring formation of the polyimide coating film tends to be poor.Accordingly, the polymerization degree of the formed product in thepresent invention is preferably from 0.05 to 5.0 dl/g (inN-methylpyrrolidone at a temperature of 30° C. at a concentration of 0.5g/dl) as calculated as the reduced viscosity of the polyamic acidsolution.

Specific examples of the solvent to be used for the solutionpolymerization, include N-methyl-2-pyrrolidone, N,N-dimethylformamide,N,N-dimethylacetamide, N-methylcaprolactam, dimethylsulfoxide,tetramethylurea, pyridine, dimethylsulfone, hexamethylphosphoramide andbutyrolactone. They may be used alone or as a mixture. Further, asolvent dissolving no polyimide precursor may be added to the abovesolvent within a range where a uniform solution can be obtained. Thereaction temperature for the solution polymerization can be selectedoptionally within a range of from −20° C. to 150° C., preferably from−5° C. to 100° C.

In the case where the treating agent for liquid crystal alignment of thepresent invention is used as a solvent-soluble polyimide solution, itsproduction method is not particularly limited, and a polyamic acidobtained by reacting a tetracarboxylic dianhydride with a diamine, maybe imidized directly in the solution to obtain the solvent-solublepolyimide solution. In this case, to convert the polyamic acid into apolyimide, a method of dehydration ring-closure by heating or a methodof chemical ring-closure by means of a known dehydration ring-closurecatalyst, may be employed. In the method by heating, the temperature canbe selected optionally within a range of from 100° C. to 300° C.,preferably from 120° C. to 250° C. In the method of chemicalring-closure, e.g. pyridine or triethylamine may be used in the presenceof e.g. acetic anhydride, and the temperature in this case can beselected optionally within a range of from −20° C. to 200° C.

The polyimide solution thus obtained may be used directly, or thepolyimide may be used as a powder precipitated and isolated from a poorsolvent such as methanol or ethanol, or the polyimide powder may beredisssolved in a suitable solvent. The solvent for redissolution is notparticularly limited so long as it dissolves the obtained polyimide, andspecific examples of which include 2-pyrrolidone, N-methylpyrrolidone,N-ethylpyrrolidone, N-vinylpyrrolidone, N,N-dimethylacetamide,N,N-dimethylformamide and γ-butyrolactone.

Further, even a solution dissolving no polymer by itself, may be addedto the above solvent within a range of not impairing the solubility.Specific examples of which include ethylcellosolve, butylcellosolve,ethylcarbitol, butylcarbitol, ethylcarbitol acetate, ethylene glycol,1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-butoxy-2-propanol,1-phenoxy-2-propanol, propylene glycol monoacetate, propylene glycoldiacetate, propylene glycol-1-monomethylether-2-acetate, propyleneglycol-1-monoethylether-2-acetate, dipropylene glycol,2-(2-ethoxypropoxy)propanol, methylester lactate, ethylester lactate,n-propylester lactate, n-butylester lactate and isoamylester lactate.

The content of the polyamic acid or the solvent-soluble polyimide in thetreating agent for liquid crystal alignment of the present inventionthus obtained, is not particularly limited so long as the solution isuniform. However, it is usually from 1 to 15 wt %, preferably from 2 to8 wt %, as a solid content.

Further, with a purpose of further improving the adhesive properties ofa polyimide resin film to a substrate, an additive such as a couplingagent may be added to the obtained resin solution.

The treating agent for liquid crystal alignment of the present inventionis coated on a transparent substrate of e.g. glass or plastic providedwith transparent electrodes, followed by baking, to prepare a polyimidefilm, and its surface is subjected to rubbing treatment to obtain aliquid crystal alignment film. As the method of coating the treatingagent for liquid crystal alignment, a known method such as spin coatingor flexographic printing may, for example, be employed.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted thereto.

Here, bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylic dianhydride used inExamples was one having a content of the isomer [IV] of 97%.

Example 1

4.50 g (0.018 mol) of bicyclo[3,3,0]octane-2,4,6,8-tetracarboxylicdianhydride (hereinafter referred to simply as BODA), 0.68 g (0.0018mol) of 4-(4-trans-n-pentylcyclohexylphenoxy)-1,3-diaminobenzene and1.75 g (0.0162 mol) of p-phenylenediamine were reacted in 39.3 g ofN-methylpyrrolidone (hereinafter referred to simply as NMP) at roomtemperature, and further reacted at 40° C. for 43 hours. The reducedviscosity of the obtained polyamic acid was 0.97 dl/g (0.5 g/dl, in NMPat 30° C.).

To 42 g of this polyamic acid solution, NMP was added to prepare asolution of 1 wt %, and 4.18 g of acetic anhydride and 6.48 g ofpyridine as imidization catalysts were added thereto, followed byreaction at room temperature for 30 minutes and at 120° C. for 2 hours.This solution was introduced into a large amount of methanol, and theobtained white precipitate was collected by filtration and dried toobtain a white polyimide powder. The imidization degree of the obtainedpolyimide powder was measured, and it was 72%.

0.6 g of this powder was dissolved in 9.4 g of γ-butyrolactone toprepare a solution having a solid content concentration of 6 wt %. Thissolution was flexographically printed on a glass substrate provided withtransparent electrodes, whereupon a uniform coating film was obtained.

Further, this solution was spin coated at 3,500 rpm on a glass substrateprovided with transparent electrodes followed by baking at 200° C. for 1hour to prepare a polyimide film having a film thickness of 100 nm. Thiscoating film was rubbed with a cloth, and the surface appearance of thealignment film was observed by a microscope, whereupon no separation orabrasion was seen.

Then, to measure electrical properties of the liquid crystal cell, usingsubstrates having a polyimide film formed and rubbed in the same manneras above, spacers of 6 μm were spread on the film surface, then thesubstrates were fabricated so that the rubbing directions would be atright angles, and liquid crystal MLC-2003 (manufactured by Merck Co.) orZLI-2293 (manufactured by Merck Co.) was injected to prepare a 90° C.twist liquid crystal cell. The alignment state of the liquid crystal inthis cell was observed by a polarization microscope to confirm a uniformalignment without defects.

With respect to this liquid crystal cell, the voltage holding ratio wasmeasured and found to show a high voltage holding property of 99% at 23°C. and 85% at 90° C. with respect to the liquid crystal cell usingMLC-2003, and 98% at 23° C. and 70% at 90° C. with respect to the liquidcrystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 4.1° with respect to the liquidcrystal cell using MLC-2003.

Example 2

To the polyamic acid solution of 1 wt % prepared and diluted in the samemanner as in Example 1, 4.18 g of acetic anhydride and 6.48 g ofpyridine were added and reacted at room temperature for 30 minutes andat 120° C. for 4 hours. This solution was introduced into a large amountof methanol, and the obtained white precipitate was collected byfiltration and dried to obtain a white polyimide powder. The imidizationdegree of the obtained polyimide powder was measured, and it was 80%.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 85% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 76% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 4.0° with respect to the liquidcrystal cell using MLC-2003.

Example 3

4.50 g (0.018 mol) of BODA, 0.68 g (0.0018 mol) of4-(4-trans-n-pentylcyclohexylphenoxy)-1,3-diaminobenzene and 3.21 g(0.0162 mol) of 4,4′-diaminodiphenylethane were reacted in 47.5 g of NMPat room temperature for 48 hours to obtain a polyamic acid solutionhaving a reduced viscosity of 0.91 dl/g (0.5 g/dl, in NMP at 30° C.).

To 42 g of this polyamic acid solution, NMP was added to prepare asolution of 1 wt %, and 4.18 g of acetic anhydride and 6.48 g ofpyridine as imidization catalysts were added thereto, followed byreaction at room temperature for 30 minutes and at 120° C. for 2 hours.This solution was introduced into a large amount of methanol, and theobtained white precipitate was collected by filtration and dried toobtain a white polyimide powder. The imidization degree of the obtainedpolyimide powder was 70%.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 84% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 70% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 2.7° with respect to the liquidcrystal cell using MLC-2003.

Example 4

4.50 g (0.018 mol) of BODA, 1.36 g (0.0036 mol) of4-(4-trans-n-pentylcyclohexylphenoxy)-1,3-diaminobenzene and 1.56 g(0.0144 mol) of p-phenylenediamine were reacted in 39.3 g of NMP at roomtemperature for 48 hours to obtain a polyamic acid solution having areduced viscosity of 0.90 dl/g (0.5 g/dl, in NMP at 30° C.).

To 10.5 g of this polyamic acid solution, NMP was added to prepare asolution of 1 wt %, and 1.05 g of acetic anhydride and 1.62 g ofpyridine as imidization catalysts were added thereto, followed byreaction at room temperature for 30 minutes and at 105° C. for 2 hours.This solution was introduced into a large amount of methanol, and theobtained white precipitate was collected by filtration and dried toobtain a white polyimide powder. The imidization degree of the obtainedpolyimide powder was 50%.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 83% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 75% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Example 5

To the polyamic acid solution of 1 wt % prepared and diluted in the samemanner as in Example 4, 1.05 g of acetic anhydride and 1.62 g ofpyridine were added and reacted at room temperature for 30 minutes andat 120° C. for 2 hours. This solution was introduced into a large amountof methanol, and the obtained white precipitate was collected byfiltration and dried to obtain a white polyimide powder. The imidizationdegree of the obtained polyimide powder was 72%.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 88% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 82% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Example 6

To the polyamic acid solution of 1 wt % prepared and diluted in the samemanner as in Example 4, 1.26 g of acetic anhydride and 0.21 g oftriethylamine were added and reacted at room temperature for 30 minutesand at 120° C. for 2 hours. This solution was introduced into a largeamount of methanol, and the obtained white precipitate was collected byfiltration and dried to obtain a white polyimide powder. The imidizationdegree of the obtained polyimide powder was 90%.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 86% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 80% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Example 7

4.50 g (0.018 mol) of BODA, 1.36 g (0.0036 mol) of4-hexadecanoxy-2.4-diaminobenzene and 1.56 g (0.0144 mol) ofp-phenylenediamine were reacted in 39.3 g of NMP at room temperature for48 hours to obtain a polyamic acid solution having a reduced viscosityof 0.96 dl/g (0.5 g/dl, in NMP at 30° C.).

To 42 g of this polyamic acid solution, NMP was added to prepare asolution of 1 wt %, and 4.18 g of acetic anhydride and 6.48 g ofpyridine as imidization catalysts were added thereto, followed byreaction at room temperature for 30 minutes and at 120° C. for 2 hours.This solution was introduced into a large amount of methanol, and theobtained white precipitate was collected by filtration and dried toobtain a white polyimide powder. The imidization degree of the obtainedpolyimide powder was 72%.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 83% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 76% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 5.5° with respect to the liquidcrystal cell using MLC-2003. Further, rectangular waves of 30 Hz/±3Vhaving a direct current of 3V superimposed thereon were applied to theliquid crystal cell at 23° C. for 60 minutes, and immediately after thedirect current voltage was cut off, the residual DC voltage remaining inthe liquid crystal cell was measured by an optical flicker eliminationmethod and found to be 1.1V.

Example 8

4.37 g (0.0175 mol) of BODA, 0.38 g (0.001 mol) of n-octadecylsuccinicanhydride, 1.56 g (0.0144 mol) of p-phenylenediamine, 0.71 g (0.0030mol) of 4,4′-diaminodiphenylmethane and 1.36 g (0.0036 mol) ofhexadecanoxy-2,4-diaminobenzene were reacted in 39.8 g of NMP at roomtemperature for 48 hours to obtain a polyamic acid solution having areduced viscosity of 0.90 dl/g (0.5 g/dl, in NMP at 30° C.).

To 42 g of this polyamic acid solution, NMP was added to prepare asolution of 1 wt %, and 4.18 g of acetic anhydride and 6.48 g ofpyridine as imidization catalysts were added thereto, followed byreaction at room temperature for 30 minutes and at 120° C. for 2 hours.This solution was introduced into a large amount of methanol, and theobtained white precipitate was collected by filtration and dried toobtain a white polyimide powder. The imidization degree of the obtainedpolyimide powder was 72%.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 85% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 81% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 5.3° with respect to the liquidcrystal cell using MLC-2003.

Example 9

4.50 g (0.018 mol) of BODA, 1.56 g (0.0144 mol) of p-phenylenediamine,0.36 g (0.0018 mol) of 4,4′-diaminodiphenylmethane and 0.68 g (0.0018mol) of 4-hexadecanoxy-2,4-diaminobenzene were reacted in 46.4 g of NMPat room temperature for 48 hours to obtain a polyamic acid solutionhaving a reduced viscosity of 0.92 dl/g (0.5 g/dl, in NMP at 30° C.).

To 42 g of this polyamic acid solution, NMP was added to prepare asolution of 1 wt %, and 4.18 g of acetic anhydride and 6.48 g ofpyridine as imidization catalysts were added thereto, followed byreaction at room temperature for 30 minutes and at 120° C. for 2 hours.This solution was introduced into a large amount of methanol, and theobtained white precipitate was collected by filtration and dried toobtain a white polyimide powder. The imidization degree of the obtainedpolyimide powder was 70%.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 86% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 80% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Example 10

10.81 g (0.1 mol) of p-phenylenediamine was dissolved in 203 g of NMP,and 19.22 g (0.98 mol) of cyclobutanetetracarboxylic dianhydride wasadded thereto, followed by reaction at room temperature for 4 hours toobtain a polyamic acid solution having a reduced viscosity of 0.98 dl/g(0.5 g/dl, in NMP at 30° C.). This solution was diluted to have a solidcontent concentration of 6 wt % to obtain a polyamic acid solution(A-1).

The polyamic acid solution (A-1) was mixed with the soluble polyimidesolution (S-1) having a solid content concentration of 6 wt %,polymerized and imidized in Example 7, with a weight ratio of (S-1) to(A-1) of 1 to 4, and adequately stirred to obtain a uniform solution.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 81% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 73% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 6.0° with respect to the liquidcrystal cell using MLC-2003. Further, rectangular waves of 30 Hz/±3Vhaving a direct current of 3V superimposed thereon were applied to theliquid crystal cell at 23° C. for 60 minutes, and immediately after thedirect current voltage was cut off, the residual DC voltage remaining inthe liquid crystal cell was measured by an optical flicker eliminationmethod and found to be 0.1V.

Example 11

20.02 g (0.1 mol) of 4,4′-diaminodiphenyl ether was dissolved in 225 gof NMP, and 19.22 g (0.98 mol) of cyclobutanetetracarboxylic dianhydridewas added thereto, followed by reaction at room temperature for 4 hoursto obtain a polyamic acid solution having a reduced viscosity of 0.98dl/g (0.5 g/dl, in NMP at 30° C.). This solution was diluted to have asolid content concentration of 6 wt % to obtain a polyamic acid solution(A-2).

The polyamic acid solution (A-2) was mixed with the soluble polyimidesolution (S-1) having a solid content concentration of 6 wt %,polymerized and imidized in Example 7, with a weight ratio of (S-1) to(A-2) of 1 to 4, and adequately stirred to obtain a uniform solution.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 82% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 81% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 6.1° with respect to the liquidcrystal cell using MLC-2003. Further, rectangular waves of 30 Hz/±3Vhaving a direct current of 3V superimposed thereon were applied to theliquid crystal cell at 23° C. for 60 minutes, and immediately after thedirect current voltage was cut off, the residual DC voltage remaining inthe liquid crystal cell was measured by an optical flicker eliminationmethod and found to be 0.2V.

Example 12

19.83 g (0.1 mol) of 4,4′-diaminodiphenylmethane was dissolved in 224 gof NMP, and 19.22 g (0.98 mol) of cyclobutanetetracarboxylic dianhydridewas added thereto, followed by reaction at room temperature for 4 hoursto obtain a polyamic acid solution having a reduced viscosity of 0.96dl/g (0.5 g/dl, in NMP at 30° C.). This solution was diluted to have asolid content concentration of 6 wt % to obtain a polyamic acid solution(A-3).

The polyamic acid solution (A-3) was mixed with the soluble polyimidesolution (S-1) having a solid content concentration of 6 wt %,polymerized and imidized in Example 7, with a weight ratio of (S-1) to(A-3) of 1 to 4, and adequately stirred to obtain a uniform solution.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 82% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 81% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 6.0° with respect to the liquidcrystal cell using MLC-2003. Further, rectangular waves of 30 Hz/±3Vhaving a direct current of 3V superimposed thereon were applied to theliquid crystal cell at 23° C. for 60 minutes, and immediately after thedirect current voltage was cut off, the residual DC voltage remaining inthe liquid crystal cell was measured by an optical flicker eliminationmethod and found to be 0.2V.

Example 13

20.02 g (0.1 mol) of 4,4′-diaminodiphenyl ether was dissolved in 255 gof NMP, and 25.02 g (0.1 mol) of BODA was added thereto, followed byreaction at room temperature for 24 hours to obtain a polyamic acidsolution having a reduced viscosity of 0.97 dl/g (0.5 g/dl, in NMP at30° C.). This solution was diluted to have a solid content concentrationof 6 wt % to obtain a polyamic acid solution (A-4).

The polyamic acid solution (A-4) was mixed with the soluble polyimidesolution (S-1) having a solid content concentration of 6 wt %,polymerized and imidized in Example 7, with a weight ratio of (S-1) to(A-4) of 1 to 4, and adequately stirred to obtain a uniform solution.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to show a high voltage holding property of 99%at 23° C. and 84% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 82% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method, and found to be 6.0° with respect to the liquidcrystal cell using MLC-2003. Further, rectangular waves of 30 Hz/±3Vhaving a direct current of 3V superimposed thereon were applied to theliquid crystal cell at 23° C. for 60 minutes, and immediately after thedirect current voltage was cut off, the residual DC voltage remaining inthe liquid crystal cell was measured by an optical flicker eliminationmethod and found to be 0V.

Example 14

The polyamic acid solution polymerized in Example 4 was diluted with NMPto prepare a polyamic acid solution (A-5) of 6 wt %.

Further, the polyamic acid solution (A-5) was mixed with the solublepolyimide solution (S-2) having a solid content concentration of 6 wt %,polymerized and imidized in Example 8, with a weight ratio of (S-2) to(A-5) of 1 to 4, and adequately stirred to obtain a uniform solution.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to shown a high voltage holding property of 99%at 23° C. and 83% at 90° C. with respect to the liquid crystal cellusing MLC-2003, and 98% at 23° C. and 80% at 90° C. with respect to theliquid crystal cell using ZLI-2293.

Further, the tilt angle of the liquid crystal cell was measured bycrystal rotation method and found to be 6.0° with respect to the liquidcrystal cell using MLC-2003.

Example 15

The polyamic acid solution polymerized in Example 4 was diluted with NMPto prepare a polyamic acid solution (A-5) of 6 wt %.

Further, the polyamic acid solution (A-5) was mixed with the solublepolyimide solution (S-4) having a solid content concentration of 6 wt %,polymerized and imidized in Example 10, with a weight ratio of (S-4) to(A-5) of 1 to 4, and adequately stirred to obtain a uniform solution.

Then, a polyimide film was prepared in the same manner as in Example 1,and the printing property state was observed to confirm that a uniformcoating film was obtained. Further, after rubbing, the surfaceappearance of the film was confirmed by a polarization microscope,whereupon no separation or abrasion of the film due to rubbing was seen.Further, the voltage holding property of the liquid crystal cell wasevaluated and confirmed to shown a high voltage holding property of 99%at 23° C. and 83% at 90° C. with respect to the liquid crystal cellusing MLC-2003.

Comparative Example 1

30.3 g (0.1 mol) of3,4-dicarboxy-1,2,3,4-tetrahydro-1-naphthalenesuccinic dianhydride, 9.72g (0.09 mol) of p-phenylenediamine and 3.48 g (0.01 mol) of1-hexadecanoxy-2,4-diaminobenzene were reacted in 245 g of NMP at roomtemperature for 10 hours, to prepare a polyamic acid solution.

To 50 g of this polyamic acid solution, 10.8 g of acetic anhydride and5.0 g of pyridine as imidization catalysts were added, followed byreaction at 50° C. for 3 hours to prepare a polyimide solution. Thissolution was introduced into a large amount of methanol, and theobtained white precipitate was collected by filtration and dried toobtain a white polyimide powder. The imidization degree of the obtainedpolyimide powder was 90%.

0.6 g of this powder was dissolved in 9.4 g of γ-butyrolactone toprepare a solution having a solid content concentration of 6%. Thissolution was spin coated at 3,000 rpm on a glass substrate provided withtransparent electrodes, followed by baking at 200° C. for 1 hour toobtain a polyimide film having a film thickness of 100 nm.

This coating film was rubbed under the same condition as in Example 1,and the surface appearance of the alignment film was observed by meansof a microscope, whereupon abrasion of the film was seen. A liquidcrystal cell was prepared in the same manner as in Example 1 by usingthis polyimide film, whereupon the tilt angle was 5.0°.

Further, the voltage holding ratio of a twist cell prepared in the samemanner as in Example 1, was measured and found to be 97% at 23° C. and42% at 105° C. with respect to the liquid crystal cell using MLC-2003and 96% at 23° C. and 49% at 80° C. with respect to the liquid crystalcell using ZLI-2293, and the voltage holding ratio was low particularlyat a high temperature.

Comparative Example 2

A twist cell was prepared in the same manner as in Example 1 using thepolyamic acid solution (A-1) prepared in Example 10, and the voltageholding ratio of the liquid crystal cell was measured and found to be94% at 23° C. and 50% at 80° C. with respect to the liquid crystal cellusing MLC-2003, and the voltage holding ratio was low particularly at ahigh temperature.

Industrial Applicability

The treating agent for liquid crystal alignment containing the polyamicacid or the solvent-soluble polyimide of the present invention, isexcellent in printing property on a substrate, and provides a liquidcrystal alignment film having no separation nor abrasion during rubbing,even in the case of the solvent-soluble polyimide. Further, the voltageholding ratio is high at a high temperature, and a liquid crystaldisplay device having a high reliability and excellent properties can beprepared.

What is claimed is:
 1. A treating agent for liquid crystal alignment,which comprises a polyamic acid compound having a reduced viscosity offrom 0.05 to 5.0 dl/g (in N-methylpyrrolidone at a temperature of 30° C.at a concentration of 0.5 g/dl) and containing repeating unitsrepresented by the general formula [I]:

(wherein R¹ is a tetravalent organic group constituting atetracarboxylic acid which has an alicyclic structure having from 2 to 5rings condensed and wherein all the carbonyl groups are directly bondedto the alicyclic structure and said carbonyl groups are not bonded toadjacent carbon atoms in the alicyclic structure, and R² is a bivalentorganic group constituting a diamine) or a polyimide compound obtainedby imidizing said polyamic acid compound.
 2. The treating agent forliquid crystal alignment according to claim 1, wherein R¹ in the generalformula [I] is a tetravalent organic group constituting atetracarboxylic acid represented by the general formula [II]:

(wherein each of X¹, X², X³ and X⁴ which are independent of one another,is a single bond or a methylene group, and m is an integer of from 1 to3).
 3. The treating agent for liquid crystal alignment according toclaim 1, wherein R¹ in the general formula [I] is a tetravalent organicgroup constituting a tetracarboxylic acid represented by the formula[III]:


4. The treating agent for liquid crystal alignment according to claim 1,wherein the formula [III] is a single component selected from isomers ofthe formulae [IV] to [VI], or a mixture thereof:


5. The treating agent for liquid crystal alignment according to claim 1,which comprises at least one member selected from polymers having animidization degree a% of 0<a≦100% of the polyimide obtained by imidizingthe polyamic acid compound represented by the general formula [I]. 6.The treating agent for liquid crystal alignment according to claim 1,wherein R² in the general formula [I] comprises a bivalent organic groupconstituting a diamine having a long chain alkyl group with a carbonnumber of at least 6, or a fluorine-containing alkyl group with a carbonnumber of at least
 6. 7. A treating agent for liquid crystal alignment,wherein the polyamic acid compound represented by the general formula[I] of claim 1 or the polyimide compound obtained by imidizing saidpolyamic acid compound, is mixed in an amount of at least 10 wt % basedon the total polymer weight, with a polyamic acid compound representedby the general formula [VII]:

wherein R³ is a tetravalent organic group constituting a tetracarboxylicacid, and R⁴ is a bivalent organic group constituting a diamine having areduced viscosity of from 0.05 to 5.0 dl/g in N-methylpyrrolidone at atemperature of 30° C. at s concentration of 0.5 g/dl.
 8. The treatingagent for liquid crystal alignment according to claim 7, wherein, in thepolyamic acid compound of the general formula [VII], R³ contains atetravalent organic group constituting an aliphatic tetracarboxylicdianhydride.
 9. A liquid crystal alignment film obtained by coating on asubstrate the treating agent for liquid crystal alignment as in one ofclaims 1-8, followed by baking, and then applying rubbing treatment tothe surface of the coating film.
 10. A liquid crystal device whichcomprises a liquid crystal alignment film obtained by coating on asubstrate the treating agent for liquid crystal alignment as in one ofclaims 1-8, followed by baking, and then applying rubbing treatment tothe surface of the coating film.
 11. The treating agent for liquidcrystal alignment according to claim 1, wherein R¹ in the generalformula [I] is a tetravalent organic group constituting atetracarboxylic acid represented by general formulas [VIII], [IX], [X]or [XI]:


12. The treating agent for liquid crystal alignment according to claim1, wherein R² is selected from the group consisting of aromaticdiamines, alicyclic diamines, aliphatic diamines and silicon diamines,or mixtures thereof.